Antilisterial bacteriocin-producing strain of Lactobacillus curvatus CWBI-B28 as a preservative culture in bacon meat and influence of fat and nitrites on bacteriocins production and activity

The objectives of this study were to evaluate the effectiveness of a bacteriocin-producing Lactobacillus curvatus CWBI-B28 to inhibit the growth of Listeria monocytogenes in de Man, Rogosa and Sharp (MRS) broth and in bacon meat. A co-culture of L. monocytogenes with the Bac(+) strain in MRS broth, resulted in a reduction of the pathogen counts by 4.2 log cycles after 24h of incubation at 37 degrees C. In bacon, the counts of L. monocytogenes was reduced to below the detectable limit (< 10cfu/g) in samples inoculated with the Bac(+) strain within 1 or 2 weeks in absence or presence of nitrites (210mg/kg), respectively. However, a week later, a re-growth of the pathogen has occurred. In contrast, no such reduction in Listeria cfus was observed in samples treated with the Bac(-) derivative of Lb. curvatus CWBI-B28. Nonetheless, the extent of inhibitory effect of the Bac(+) strain against L. monocytogenes in bacon was somewhat reduced in the presence of nitrites. A separate study on the influence of nitrites and fats on growth and bacteriocin production by Lb. curvatus CWBI-B28 revealed that the curing agent affects the growth of the Bac(+) strain and, thereby bacteriocin production and activity only at concentrations (> 5%) far beyond those allowed in the meat industry. Fat content did not affect the bacterial growth even at the highest concentration used (i.e. 50%), however, it interfered significantly with the detection of AUs and the antilisterial activity. Use of the Bac(+) Lb. curvatus CWBI-B28 has proven efficient in controlling L. monocytogenes in bacon despite the slight antagonistic effect of nitrites, however the efficacy was dramatically reduced upon extended period of storage at 4 degrees C.